Method of analysis with radioactive material



Patented Dec. 19, 1944'- METHOD OF ANALYSIS WITH RADIOACTIVE MATERIAL raid E. Hill, Forest Hills, Pa., asslgnor to Westhouse Electric & Manufacturing Company,

East Pittsburgh, Pa., a corporation of lennsyb, vanla No Drawing. Application June 17, 1942,

Serial No. 447,469

11 Claims.

. placed in a furnace and subjected to extremely high temperatures in the presence of certain agents whereby the concentration of various elements in the metal is reduced to a desired value. This procedure is followed in the production of steel in which phosphorus and carbon are the major elements the concentrations of which are '-.to be controlled. Atvarious times during the refining process, samples of the steel are analyzed to determine the percentages of carbon and phosphorus therein. The analysis is then furnished to the furnace operator so that he may take proper steps for controlling the com-' position oi the finished steel. as well as reducing the overall time reouired'ior the refining. It is highly desirable that the results of the analysis be made available to the operator very quickly after the taking of the sample. The quicker the information is received, the closer the operator can maintain conditions to the point of maximum ei'liciency in producing a steel of the desired composition.

Various methods have men devised for determining the percentage of carbon present in the steel, and some of these methods permit a rapid analysis to be made. However, the phosphorus content of the steel is customarily determined at various times during the refining by the regular chemical method which requires approximately one and one-half hours for each analysis. The

where chemical concentrations are to be carefully controlled.

It is accordingly an, object of my invention to provide a method for rapidly determining the concentration of an element in a mass while the mass is subjected to treatment wherein the concentration is reduced.

A further object of my invention is to provide a method for rapidly and inexpensively analyzing the concentration of an element in a metal at various times during the refining thereof.

Another object of my invention is to provide an accurate method for rapidly determining the concentration of phosphorus in steel at various times during the refining thereof.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, together with additional objects and advantages thereof will best be understood from the following description of a specific application of the invention.

My invention may be advantageously employed in the determination. of the phosphorus content radioactive phosphorus is added to the charge oi time required ior' completion or the analysis is Y critical point may pass while the operator is waiting for the-results of the analysis. This is especially true if it is desired to produce a steel 11thisi composition of which is specified within close ts. a The necessity ior speed in making an analysis is also apparent in the production of certain ther alloys or in the production of any material of steel at various times during the refining of the steel in an open-hearth furnace. In accordance with my invention, a small quantity of the furnace. To prevent any substantial loss of the radioactive phosphorus prior'to its reduction by the usual operation of the open-hearth process, the radioactive phosphorus may be enclosed in a tightly sealed steel chamber. By the time the chamber melts, the charge is in a molten state and the radioactive phosphorus is thoroughly mixed therewith. Of course other methods of introducing the radioactive phosphorus may be used. Thereafter theamount of radio-- active phosphorus in the steel is reduced in diable quantity is drawn of! and its radioactivity A is measured with any si'iitable device, such as a Geiger-Mueller counter, an ionization chamber, or an electroscope. The same sample or one drawn at the same time is subjected to a chemical analysis to determine the percentage of phosphorus present in the steel. Thus the relationship between theradioactlvity of the steel and the concentration of the phosphorus may be established. Thereafter samples of an equal quantity are drawn oil! at the various desired times. The radioactivity of each sample is measured. Then, as the relationship between I twelve furnaces.

the radioactivity of the steel and the concentration of the phosphorus is known, the percentage of phosphorus at the time of taking the sample may be derived.

By experiment, it has been discovered that approximately 0.15 millicuries of radioactive phosphorus per ton of steel is sufficient to give a counting rate of ten counts per second, using a Geiger-Mueller counter with a 1% inch sensitive tube length. Under such] circumstances, measurements for only a two-minute period enables a determination of the amount of Phosphorus present within 3% of the phosphorus regardles's of the amount of phosphorus per unit of steel. In addition, the accuracy can befurther increased by increasing the amount of radioactive material used and/or by increasing the length of the measurement period. The accuracy thus available through the radioactive method compares favorably with that obtainable by the regular chemical method. Since the accuracy of the chemical method varies with the amount of phosphorus per unit of steel and that of the radioactive method does not, the latter is particularly advantageous when the percentage of phosphorus is low.

The great advantage of the radioactive method over the regular chemical method is that the concentration of phosphorus in the steel can be followed more closely because of the short time required for analysis. As the timerequired to measure the radioactivity of each sample is approximately three to four minutes after the sample has been prepared, one man can easily measure a sample every hour from each of ten or The time to prepare the sample is not greater than that to prepare a sample for the chemist. Therefore, the measurement time of three to four minutes for the radioactive method is to be compared with one and one-half hours for regular chemical analysis. As a result, the furnace operators are supplied with information which is sufliciently timely to enable them to increase the efficiency of the refining process. In addition to the saving inexpenses afforded by an increase in the efliciency of the furnace operation, there is also-a saving in the cost of making the necessary analysis as fewer chemists ae needed than if the analysis were made by the chemical method alone.

It is apparent that the advantages to be derived from the use of this method of analysis are not confined to the determination of the phosphorus content in producing open-hearth steel. It is well known that the production of other metals, alloys and other materials require careful control of the chemical concentration of a. particular element. If that element can be made radioactive in a form such that its reduction will be directly proportional to the reduction of the main body ofthe element, this methd of analysis may be employed to advantage. Further, if a suitable radioactive isotope of the particular element to be followed is not available, a radioactive isotope of another element may be used in the practice of this method providing the chemical behavior of the other element is such that there would be a definite known relationship in the change in concentration of the other element and the element to be followed.

Although I have shown and described a specific application of my invention, I am fully aware that many other applications thereof are possible. My invention. therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of determining the concentration of an element in a mass at'various times while the mass is subjected to a treatment which tends to change the concentration of said element in said mass, a portion only of said element in the mass being radioactive, which comprisesdetermining the relationship between radioactivity of the mass and concentration of the element and subsequently measuring the radioactivity of the mass at said various times whereby the concentration at each of said times may be derived from said relationship.

2. The method of determining the concentration of an element in a mass at various times while the mass is subjected to a treatment which tends to change the chemical equilibrium between said element and other components of said mass, a portion only of said element in the' mass being radioactive, which comprises measuring the radioactivity of the mass and determining by chemical analysis the concentration of the element in the mass as composed when the radioactivity is measured to establish the relationship between radioactivity of the mass and concentration of the element, and subsequently measuring the radioactivity of the mass at said various times whereby the concentration at each of said times may be derived from said relationship.

3. The method ofdetermining the concentration of an element in a mass at various times while the mass is subjected to a treatment at high temperatures wherein the concentration is changed, a portion of said element in the mass being radioactive and the concentration of the element being known prior to said treatment, which comprises measuring the radioactivity of the mass prior to said treatment to establish the relationship between radioactivity of the mass and concentration of the element and subsequently measuring the radioactivity of the mass at said various times, whereby the concentration at each of said times may be derived from said relationship.

4. The method of determining the concentration of an element in a normally non-radioactive mass at various times while the mass'is sub- Jected to a treatment wherein the concentration is reduced, which comprises mixing a small quantity of the same element which is radioactive at said various times whereby the concentration at each of said times may be derived from said relationship. 3

5. The method of determining the concentration of an element in a normally non-radioactive mass at various times while the mass is subjected to treatment wherein. the concentration is reduced, which comprises mixing a small quantity of a radioactive material in the mass having such a. chemical behavior that the concentration of the material is reduced in a definite relationship to the reduction in concentration of said element, determining the relationship between radioactivity of the mass and concentration of said element and subsequently measuring the radioassasos activity or the mass at said various times where-- of the same element which is radioactive in the mass in a form such that the concentration of the radioactive portion is decreased in direct proportion to the decrease in concentration of i the rest of the element, then measuring the radioactivity of the mass and determining by chemical analysis the concentration of said element in the masses composed when the radioactivity is measured to establish the relationship between radioactivity of the mass and concentration of the element, and subsequently measuring the radioactivity of the mass at said various times, whereby the concentration at each of said times may be derived from said relationship.

7. The method of determining the concentration of an element in a metal at various times during the refining thereof wherein the concentration is reduced, the metal being in a molten state with a portion of said element being radioactive, which comprises determining the relationship between radioactivity of the'metal and concentration of the element and subsequently measuring the radioactivity of the metal atsaid various times, whereby the concentration at each whereby the concentration at each of col may be derived from said relationship.

9. The method of determining the concentra tion oi phosphorus in steel at various times dur= ing the refining thereof wherein the concentra tion is reduced, the steel being in a molten state with a portion of said phosphorus being radioactive, which comprises determining the relationship between radioactivity of the steel and concentration of the phosphorus and subsequently measuring the radioactivity of the steel at said various times, whereby the concentration at each of said times may be derived from said relationship.

10. The method of determining the concen- 7 tration of phosphorus in steel at various times during the refining thereof wherein the concentration is reduced, the steel being in a molten state with a portion of said phosphorus being radioactive, which comprises measuring the radioactivity of the steel and determining by chemical analysis the concentration of the phosphorus in the steel as composed when the radioct said times may be derived from said relationactivity is measured to establish the relationship between radioactivity oi the metal and concentration of the phosphorus, and subsequently measuring the radioactivity of the steel at said various times, whereby the concentration at each oi'said times may be derived from said relationship.

11. The method of determining the concentration of phosphorus in steel at various times during the refining thereof by the open-hearth process, which comprises adding a small quantity of radioactive phosphorus to the steel, then measuring the radiactivity of the steel and determining by chemical analysis the concentration of phosphorus in the steel as composed when the radioactivity is measured toestablish the relationship between radioactivity of the steel and concentration of the phosphorus, and subsequently maesuring the radioactivity of the steel at said various times. whereby the concentration at each of said times may be derived 45 from said relationship.

JERALD nmn 

